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Periodization is the systematic planning of athletic or physical training. It involves progressive cycling of various aspects of a training program during a specific period. It is a way of alternating training to its peak during season. The aim of periodization is to introduce new movements as one progresses through the macrocycle to specify one's training right up until the start of the season.[clarification needed]
The roots of periodization come from Hans Selye’s model, known as the General adaptation syndrome (GAS), describing biological responses to stress. Selye's work has been used by the athletic community since the 1950s (Fleck, 1999).
The GAS describes three basic stages of response to stress: (a) the Alarm stage, involving the initial shock of the stimulus on the system, (b) the Resistance stage, involving the adaptation to the stimulus by the system, and (c) the Exhaustion stage, in that repairs are inadequate, and a decrease in system function results. The foundation of periodic training is keeping ones body in the resistance stage without ever going into the exhaustion stage. By adhering to cyclic training the body is given adequate time to recover from significant stress before additional training is undertaken. The response to a new stress is to first respond poorly and the response drops off. For example when the body is first exposed to sun a sunburn might develop. During the resistance stage adaptation improves the response to a higher level, called super compensation, than the previous equilibrium. The example would be that a suntan develops. The exhaustion stage is a continuation of the stimulus at too high a level and the increase gained from adaptation is now offset and all gains are lost. The example would be that wrinkles, spots, or even skin cancer develop. The goal in sports periodization is to reduce the stress at the point where the resistance stage ends so the body has time to recover. In this way the exhaustion stage does not reduce the gains achieved, the body can recover and remain above the original equilibrium point. The next cycle of increased stimulus now improves the response further and the equilibrium point continues to rise after each cycle.
Selye (1957) labeled beneficial stresses as "eustress" and detrimental stresses as "distress". In athletics, when physical stress is at a healthy level (eustress), an athlete experiences muscular strength and growth, while excessive physical stress (distress) can lead to tissue damage, disease, and death. Periodization is most widely used in resistance program design to avoid over-training and to systematically alternate high loads of training with decreased loading phases to improve components of muscular fitness (e.g. strength, strength-speed, and strength-endurance).
Russian physiologist Leo Metveyev and Romanian sport scientist Tudor Bompa expanded and further organized the periodization model. Bompa and Metveyev have been regarded as the fathers of modern periodization. Since the 1960s, other coaches and exercise physiologists have added to the original models, creating “modified” periodization models. However, despite the differing terminology amongst scientist and practitioners, the scientific basis for periodization remains a common ground.
Periodic training systems typically divide time up into three types of cycles: microcycle, mesocycle, and macrocycle. The microcycle is generally up to 7 days. The mesocycle may be anywhere from 2 weeks to a few months, but is typically a month. A macrocycle refers to the overall training period, usually representing a year or two. There are longer cycles as well for the Olympian, being 4 or 8 years, and the career plan which is usually only considered for Olympians and professional athletes.
Theory of planning 
Training should be organized and planned in advance of a competition or performance. It should consider the athlete’s potential, his/her performance in tests or competition, and calendar of competition. It has to be simple, suggestive, and above all flexible as its content can be modified to meet the athletes rate of progress.
The macrocycle 
A macrocycle refers to an annual plan that works towards peaking for the goal competition of the year. There are three phases in the macrocycle: preparation, competitive, and transition.
The entire preparation phase should be around 2/3 to 3/4 of the macrocycle. The preparation phase is further broken up into general and specific preparation of which general preparation takes over half. An example of general preparation would be building an aerobic base for an endurance athlete such as running on a treadmill and learning any rules or regulations that would be required such as proper swimming stroke as not to be disqualified. An example of specific preparation would be to work on the proper form to be more efficient and to work more on the final format of the sport, which is to move from the treadmill to the pavement.
The competitive phase can be several competitions, but they lead up to the main competition with specific tests. Testing might include any of the following: performance level, new shoes or gear, a new race tactic might be employed, pre-race meals, ways to reduce anxiety before a race, or the length needed for the taper. When the pre-competitions are of a higher priority there is a definite taper stage while lower priority might simply be integrated in as training. The competitive phase ends with the taper and the competition.
The transition phase is important for psychological reasons, a year of training means a vacation is in order. A typical weekend warrior might take three months while a professional athlete might take as little as two weeks.
The mesocycle 
A mesocycle represents a phase of training with a duration of between 2 – 6 weeks or microcycles, but this can depend on the sporting discipline. During the preparatory phase, a mesocycle commonly consists of 4 – 6 micro-cycles, while during the competitive phase it will usually consist of 2 – 4 micro-cycles depending on the competition’s calendar.
The goal of the planner is to fit the mesocycles into the overall plan timeline-wise to make each mesocycle end on one of the phases and then to determine the workload and type of work of each cycle based on where in the overall plan the given mesocycle falls. The goal in mind is to make sure the body peaks for the high priority competitions by improving each cycle along the way.
The microcycle 
A microcycle is typically a week because of the difficulty in developing a training plan that does not align itself with the weekly calendar. Each microcycle is planned based on where it is in the overall macrocycle.
The annual plan 
The annual plan is important in that it directs and guides athletic training over a year. It is based on the concept of periodization and the principles of training. The objective of training is to reach a high level of performance (peak performance) and an athlete has to develop skills, biomotor abilities and psychological traits in a methodical manner.
Preparatory phase 
This phase consists of the general preparation and specific preparation. Usually the general preparation is the longest of the two phases. And the specific preparation is the shortest.
Competitive phase 
This phase may contain a few main competitions each containing a pre-competitive and a main competition. Within the main competition, an uploading phase and a special preparatory phase may be included.
Transition phase 
This phase is used to facilitate psychological rest, relaxation and biological regeneration as well as to maintain an acceptable level of general physical preparation. This phase lasts between 3 – 4 weeks (maybe longer) but should not exceed 5 weeks under normal conditions and may be sports specific. It allows the body to fully regenerate so that it is prepared for the next discipline.